The present invention is directed generally to an aeration diffuser for a pressurized liquid treatment module, which allows for gas scouring of filtration membranes within the module.
To filter or other otherwise treat various types of liquid, such as seawater, wastewater and surface water, fiber membranes (“filtration membranes”) are typically used within a module to separate suspended solids and impurities from the liquid. Over time, the impurities will accumulate on a feed side or an exterior surface of the filtration membranes, thereby at least partially clogging or otherwise fouling the filtration membranes. The accumulated impurities are undesirable because they increase resistance to filtration and negatively affect the operation of the filtration membranes by increasing operating pressures or decreasing production.
The accumulation of impurities or fouling of the filtration membranes is typically controlled by physically cleaning the filtration membranes. Commonly, after a period of filtering impurities from the liquid, a physical cleaning is undertaken and the process of filtering and cleaning is repeated. Physical cleaning can include backwashing, which occurs by pumping liquid through the filtration membranes in a direction reverse to the filtration path. Another type of physical cleaning, known as forward flushing, occurs when liquid is pumped tangential to the feed side of the filtration membranes. During forward flushing, no filtration occurs and impurities are removed by a shearing force. A further type of physical cleaning is air scouring, which occurs by bubbling gas along the feed side of the filtration membranes, causing vibrations, which shake impurities loose and create localized eddies with shearing forces at the membrane surface.
To air scour the filtration membranes, conventional prior art systems inject gas (e.g., air) and liquid (e.g., water) through a single, common inlet into a module. In particular, the prior art injects feed water and air into the same opening or set of openings in a bottom of a module. While such prior art can be effective in providing and maintaining aeration to the filtration membranes, such a configuration does not necessarily optimize gas scouring efficiency, and it would be desirable to do so.
In particular, design considerations for introducing feed water into the module for filtering are different than for introducing air into the module for scouring. The opening(s) for feed water must be sufficiently large to allow for efficient draining from the module. However, if the opening(s) is/are too large, then a majority of the air leaves through only a portion of the opening or some of the openings and will not be evenly distributed throughout the module.
Therefore, it would be desirable to optimize gas (e.g., air) distribution within a module without compromising liquid (e.g., feed water) distribution within the module. In particular, it would be desirable to provide fluidically separate and distinct gas and liquid openings or passageways into the module to optimize gas and liquid distribution. The present invention accomplishes the above objectives.